Glass fiber-reinforced polymeric articles are well known for use in the circuit board industry. The articles form a support and dielectric layer for fine tracings of copper that form the electrical circuit. So-called circuit board blanks are prepared by laminating a thin copper foil to one or both major surfaces of the fiber glass-reinforced polymeric substrates under heat and pressure. Alternatively, the copper foil is placed on a fiber glass non-woven mat impregnated with a partially cured polymer, called a prepeg, followed by molding under high temperature and pressure. A suitable mask is applied to the copper surfaces of the blank to define the printed circuit configuration. The masked foil is then subjected to a chemical etching process to dissolve unmasked portions of the copper foil. The retained portions of the foil serve as the electrical contact paths of the finished circuit board.
The trend in recent years is towards miniaturization of electronic equipment and increased processing speed. This has resulted in finer circuits and increased wiring densities. As the wiring densities increase, the amount of heat generated also increases. The generation of heat is problematic for both the circuit board blank and the finished circuit board. The rate of thermal expansion of the fiber glass is very different from the polymeric matrix leading to distortion in the copper overlayer. This can create adhesion and short-circuiting problems.